It is well known that fuel rods in boiling water reactor (BWR) fuel bundles are supported on a lower tie plate and extend upwardly to an upper tie plate. Between the upper and lower tie plates, the fuel rods are supported laterally by a plurality of spacers. In some BWR, bundle designs, the upper and lower tie plates are directly connected to each other by several special fuel rods, called tie rods. These tie rods have lower end plugs which are threadably secured in the lower tie plate. The tie rods also have threaded upper end plugs which extend through the upper tie plate. Conventional nuts are used on these upper end plugs to secure the tie rods to the upper tie plate. Special lock washers are used to prevent rotation of the nuts. Specifically, the washers are formed with tabs which are bent upward to lock the nuts in position and thus prevent rotation.
The upper tie plate typically includes a handle extending upwardly from its base. To lift the fuel bundle, a grapple engages this upwardly extending handle. The weight of the fuel rods is transmitted to the lower tie plate, through the tie rods to the upper tie plate, and then to the handle.
Occasionally, a fuel bundle must be disassembled partway through its service life or at the end of its use. At such time, the lock washer tabs are bent to free the nuts, and the nuts and washers are then removed. Thereafter, the upper tie plate can be removed followed by extraction of one or more fuel rods as necessary.
The invention here relates to a different constructions for transferring the fuel bundle weight to the upper tie plate, and for latching and unlatching the upper tie plate from the fuel bundle to facilitate removal of fuel rods from the bundle.